ESD protection devices and methods of making same using standard manufacturing processes

ABSTRACT

Devices capable of protecting electronic components during the occurrence of a disturbance event using printed circuit board manufacturing techniques. A three (3) layer structure is formed comprising a polymer-based formulation sandwiched between two electrode layers. The devices can be manufactured in panel form providing high quantities of devices which can be removed from the panel and applied directly to the component to be protected. Desired patterns can be formed on either one of the electrode layers by photo-etch techniques thereby providing a process that can be tailored to a large number of applications.

TECHNICAL FIELD

The present invention relates to electronic circuit protection devicesand methods of making same. More particularly, the invention relates tothe use of standard printed circuit board manufacturing processes formass production of low profile polymer-based protection devices. Stillmore particularly, the invention relates to the manufacture ofsubstrate-less protection devices that can be custom formed for use in awide array of electronic circuit protection applications, such aselectrostatic discharge and surge suppression, with possibleimplications toward the manufacture of a complete PCB protection system.Even still more particularly, the method of making such devices takesadvantage of the vast know-how used in making printed circuit wiringboards and allows devices to be made in panels with features such asplated through-holes and multiple layers.

BACKGROUND OF THE INVENTION

The problems of static electricity and Electrostatic Discharge (ESD) arewell known and documented. In general, such problems arise from theoccurrence of electrical events that cause the transfer of charge fromone material to another creating a surge in voltage due to voltagepotential differences between the two materials. The ElectrostaticDischarge Association (ESDA), for example, cites industry experts asestimating that product losses due to static range from 8-33%. Accordingto the ESDA, others have estimated the actual cost of ESD damage to theelectronics industry as running into the billions of dollars annually.See http://www.esda.org/basics/part1.cfm.

In general, prior art methods of protecting components from ESD damageinclude some basic precautions such as proper grounding or shunting thatwill “dissipate” or discharge transient signals away from the device tobe protected. Still other methods include the use of packages andhandling techniques that will protect susceptible devices duringtransport and shipping. While such techniques have been effectively usedto shield the product from charge and to reduce the generation of chargecaused by any movement of product within the container housing thedevice to be protected, they have not completely eliminated the risk ofdamage attributed to such disturbances. Moreover, it is well known thatmore modem devices operating in the higher frequencies (GHz and above)using submicron line widths are more susceptible to damage which can notbe overcome using such methods.

Components designed to react to ESD events and provide a discharge pathto ground are known in the arts. For example, U.S. Pat. No. 6,172,590entitled “Over-voltage protection device and method for making same” toShrier et. al (Ms. Shrier is a co-inventor to the '590 patent. The '590patent is not commonly assigned to this application) describes adiscrete electrical protection device that utilizes a gap between twoelectrically conductive members attached to an electrically insulatingsubstrate. According to the '590 patent, the electrical protectiondevice can be either surface mounted or built with through-holes foraccommodating leads on an electrical connector. The '590 describes andclaims methods for making an electrical protection device that includesan electrically insulating substrate.

U.S. Pat. No. 6,310,752 entitled “Variable voltage protection structuresand method for making same” to Shrier et. al (Ms. Shrier is aco-inventor to the '752 patent. The '752 patent is not commonly assignedto this application) describes and claims a variable voltage protectioncomponent that includes a reinforcing layer of insulating materialhaving a substantially constant thickness embedded in a voltage variablematerial. According to the '752 patent, the reinforcing layer defines auniform thickness for the variable voltage protection componentresistive to compressive forces that may cause a reduction in the clampvoltage or a short in the voltage variable material. The '752 patentalso describes methods for making such a variable voltage protectioncomponent.

Prior art protection components, such as those incorporating theteachings of the '590 patent and the '752 patent, have been successfullymade and used. Generally, such components utilize a couple of electrodeswith some type of surge material interspersed between the electrodes.One electrode provides the transient signal input terminal while theother provides the discharge path to ground. A support layer known asthe substrate or reinforcement layer is used to provide the necessarystiffness permitting the component to be surface mounted orthrough-holed.

Such prior art protection components, however, suffer from severallimitations attributed to the requirement that a substrate orreinforcing layer be used. Specifically, the use of a substrate addssignificantly to the component's overall size and cost. In addition, therelatively large size and profile of such prior art protectioncomponents makes their use impractical in tight spaces where board spaceis limited. Moreover, since the substrate material is a primary expensein the manufacture of such components, the use of prior art protectioncomponents on a widespread basis can be cost prohibitive. An example ofsuch an application would be a multi-pin connector where ideally eachpin would be protected from ESD events that could damage a devicecoupled to the connector. In such an application, a prior art ESDprotection component could not be cost effectively used on each pin and,in most situations, would occupy too much board space and be too thickto be practical.

As electronic devices became faster and smaller, their sensitivity toESD increases. ESD impacts productivity and product reliability invirtually every aspect of today's electronics environment. Many aspectsof electrostatic control in the electronics industry also apply in otherindustries such as clean room applications and signal lineproliferation.

Therefore, a need exists for a cost effective protection component thatcan be more widely used across a wider range of applications. A methodof cost effectively manufacturing such a component would providenumerous advantages.

SUMMARY OF THE INVENTION

The present invention provides a cost effective method of manufacturinga substrate-less protection device. The invention also provide ainnovative protection device that can be manufactured in high volumeswithout a substrate layer.

As such, disclosed is a method of manufacturing devices capable ofprotecting electronic components during the occurrence of a disturbanceevent, the method comprising the step of attaching a disturbancereacting substance to a first electrode. Next, the first electrode ispositioned about a second electrode such that the disturbance reactingsubstance is interspersed in between. Finally, the first electrode,disturbance reacting substance, and second electrode are bonded to eachother such that a three (3) layer structure for a protection device iscreated.

Also disclosed is a method manufacturing a panel of electronic componentprotection devices. The method comprises the steps of coating a firstelectrode layer with a liquid polymer formulation having acharacteristic viscosity, drying the polymer formulation on the firstelectrode layer, and aligning the first electrode layer with a secondelectrode layer. Next, the first and second electrode layers are bondedto each other such that the liquid polymer formulation is interspersedbetween the first and second electrode layers thereby forming a panelfrom which a plurality of polymer-based protection devices can beobtained.

Further disclosed is a method of formulating a substance capable ofreacting to a disturbance event, the method comprising the step ofadding measured quantities of the following materials to a suitablepolymeric solution: conductor, antioxidant, and insulator. Next, thematerials are mixed within the polymeric solution until a desiredviscosity level is achieved. In one embodiment, the adding step isperformed using an epoxy solution that contains an approximate 75%solvent level.

An advantage of the present invention is that protection devices can bemanufactured in high volumes using well known printed circuit board(PCB) manufacturing techniques. With the present invention, a panelholding anywhere from several hundred up to many thousand protectiondevices can be achieved with a combination of mixing, coating, curing,lamination, photo etch, and electroding steps. As a result, applicationspecific designs can be readily customized and changes made quickly withminimal effort and expense.

Another advantage is that added capacitance can be limited bycontrolling the size of the electrode, formulation fillers and overallthickness of the devices.

Another advantage of the present invention is the achievement of a lowprofile protection device compared to the known prior art. For example,according to one embodiment a device profile of 5 mils is achievablecompared to known prior art protection components that occupy between 15and 30 mils.

Still another advantage of the invention is significant cost reductionscompared to the prior art due primarily to the elimination of asubstrate and use of printed wafer board technologies to create panelscontaining as many as 100,000 devices measuring 0603 mils and smaller.

And still another advantage is the ability to control the capacitance ofthe protection device by altering the nature of the fillercharacteristics utilized in the polymer. Depending on the restrictionsplaced on added capacitance for a given application, a polymerformulation with more or less capacitance can be utilized. In addition,minimum overlap can also be used to reduce added capacitance.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other advantages as well as specific embodiments will beunderstood from consideration of the following detailed description aswell as the appended drawings in which:

FIG. 1 is process flow diagram for the methods of the present inventionaccording to two embodiments;

FIG. 2 shows a 3 layer structure for a device capable of protectingcomponents made using the methods of the present invention;

FIG. 3 shows a panel of device protection components according to theinvention;

FIG. 4 is a process flow diagram for a method of utilizing PCBmanufacturing techniques to create a protection device according to theinvention;

FIG. 5 is a process flow diagram for a polymer formulation process thatcan be used to create a polymer-based protection device according to theinvention;

FIG. 6 show a multi-pin connector utilizing a protection devicesaccording to the invention;

FIG. 7 shows the performance of a protection device according to oneembodiment of the invention is shown; and

FIGS. 8 a and 8 b illustrating two embodiments of a protection deviceaccording to the invention, both of which utilize Kapton.

References in the detailed description refer to like references in thefigures unless otherwise indicated.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present invention provides a process of making a substrate-lessprotection device using standard printed circuit board (PCB)manufacturing techniques thereby allowing the manufacture of largenumber of devices relatively inexpensively. With the present invention,multiple ESD protection devices can be manufactured in panels that canbe custom formed for an unlimited number of applications. It is believedthat the process of the present invention has implications toward themanufacture of an all PCB protection system such as flex circuit withtotal ESD protection and/or as a layer in a PCB with protection providedfor sensitive integrated circuits.

Manufacturing a Protection Device in Panels Gives Maximum Yield in HighQuantities

In general, the process of building a protection device according to theinvention involves the use of a polymer-based formulation (or polymericsolution) that is coated directly on the electrodes forming theterminals of the protection device. As is well known, various materialscan comprise the electrodes of a protection device such as copper,beryllium copper, nickel, gold, silver and others. The process describedherein eliminates the need for a substrate or reinforcing layer tosupport the protection material. A disturbance reacting substance, suchas a polymer, is formulated to be sensitive to a given disturbanceevent, such as an ESD or surge event, according to the application inwhich the protection device is used. The process of building such acomponent can be readily understood by reference to FIG. 1 which is flowdiagram of the process, denoted generally as 10, of the presentinvention in its' most general sense. FIG. 1 shows that a substancecapable of reacting to a disturbance, such as a polymer-based liquid, isprepared 12 such that the liquid has a characteristic viscosity thatallows it to be coated onto, for example, an electrode material orrelease film. The stage viscosity, as is known and appreciated by thoseof ordinary skill in the art, is adjusted for coating and lamination.Therefore, by characteristic viscosity, the polymer is initially eithera B or C stage liquid epoxy of the type known to those of ordinaryskill. Next, after the liquid epoxy is formulated at step 12, it is thencoated onto an electrode 14 or onto a release film 16 according toseparate and alternate manufacturing processes both of which are part ofthe invention. In this regard, it should be understood that otherpolymers can be used to provide the breakdown functionality necessary toprovide a discharge function in response to the occurrence of adisturbance event.

At coating step 14, the polymer can be directly coated onto a variety ofmaterials which can provide appropriate electrode structures such as,for example, a sheet of copper or a sheet of Kapton pre-etched with adesired electrode pattern. Next, the polymer is B staged by allowing itto air dry on the electrode surface or by heating, step 18, so that thematerial can be further handled. Alternatively, the electrode andpolymer can be placed in an oven. Since the material is in B stage, itcan be applied to a second electrode, step 20, and bonded together, step22, through the application of heat and pressure for a C stage cure.Thus, the polymer is sandwiched between two electrodes to form a verystrong panel, step 24. The resulting structure is illustrated in FIG. 2.

The fact that a panel is formed at step 24 by sandwiching the polymerbetween two electrode means that no substrate or reinforcing layer isrequired thereby reducing significantly the cost of manufacturing.

Alternatively, using coating step 16, the polymer is coated unto arelease film which supports the polymer prior to application on theelectrode material. Preferably, the release film has the characteristicof being able to achieve a proper release of the coated polymer once itis applied to a second electrode. At this point, it may be useful to runthe release film with polymer on electrode through an oven in order toremove solvents from the polymer, step 26. Sometimes, the release filmand polymer can be run in an over prior to attachment to the electrodeand lamination. If a coating line is used, it is likely that an oven isstaged within the coating process to allow solvent dissipation. Also, acoating line allows continuous coating such that the polymer can bepumped directly on electrode or release film with high precision. Thelamination or press process causes the polymer to adhere to theelectrode layer.

Next, the electrode-polymer is pressed onto a second electrode, step 30,and the release film is pulled from the laminated structure, step 32,and a second electrode is attached, step 34. At this point, a three (3)layer structure has been formed consisting of one layer of polymerbetween two layers of electrode as shown in FIG. 2. The three (3) layerstructure receives a second heat and pressure cycle, either through acoating line laminator or press, step 36, and allowed to cure, step 40.At this point, a relatively strong panel consisting of cured polymersandwiched between the electrode layers is formed, step 24.

FIG. 2 shows a three (3) layer structure 50 with a first electrode 60 inthe form of a copper electrode layer. Other electrode materials may beused. A second electrode 62 has been patterned to reveal spaces 64thereby forming desired features. The spaces 64 can be utilized, forexample, as a solder mask for attachment. As shown, first electrode 60and second electrode 64 sandwich a disturbance reaching substance, inthis case a polymer-based formulation 66, which is interspersed therein.The polymer-based formulation 66 is capable of creating a signal pathfor the first electrode 60 to the second electrode 62 in response to theoccurrence of a disturbance event. In this case, a current path isformed via through-hole 68 which has been bored and soldered through thestructure 50.

With either coating step 14 or 16, it is possible to coat the polymerdirectly on electrodes which have been preformed with featuresappropriate for a particular application. For example, it has been foundthat a thin sheet of electrode material (on the order of 0.7 to 2.8 milcopper) can be preformed with desired features thereon so that theresulting device fits the application. This can be done by etching adesired pattern on the electrodes prior to application of the polymer.For example, the outline of a press-fit washer (not shown) that fitssnugly over a standard connector pin has been patterned using theprocess of the invention.

Thus, since adhesion is enhanced on the coated side of the electrodematerial, the present invention provides a means of forming correctpatterns on a sheet of electrode material and coating it with a polymerto produce a protection device. Moreover, using standard PCBmanufacturing processes, protection devices can be manufactured in largepanels that consist of numerous protection devices thereby drasticallyreducing manufacturing costs compared to known prior art.

FIG. 3 shows an entire panel, denoted as 100, of protection devices madeusing the process of FIG. 1 as described herein. The panel of FIG. 3shows that 20 connector arrays 102 can be obtained from a panelmeasuring approximately 2×5 inches. Each array 102 contains 40structures including 39 protection devices 110 and a ground hole 112resulting in a panel with approximately 800 devices. It should beunderstood, however, that panels of much larger size can be obtainedusing the process of the present invention to achieve panelsaccommodating tens of thousands of devices. In this way, the presentinvention provides significant cost reductions compared to the prior artdue primarily to the elimination of a substrate and use of printed waferboard technologies (such as those used to create through-hole 68) tocreate panels, such as the panel of FIG. 3.

With reference now to FIG. 4, therein is illustrated the process of thepresent invention according to one embodiment wherein features areetched after application of the polymer to the electrodes. Inparticular, it has been observed that manufacturing of protectiondevices according to the invention can be accomplished using well knownPrinted Circuit Board (PCB) manufacturing techniques after applicationof a polymer formulation, control of its thickness across the electrodesurface, and subjecting the resulting electrode-polymer-electrode 3layer structure to sufficient heat and pressure to achieve adhesion andbonding of the structure's layers. Of course, other suitable methods ofpolymer application, adhesion and bonding may be utilized all within thescope of the present invention.

As such, the process of FIG. 4, denoted generally as 150, starts outcoating one or two electrodes with a polymer, step 152. In this regard,the terms “electrode” and “electrode layers” or “electrode surfaces”shall be used interchangeably throughout. The decision to coat one ortwo electrodes depends primarily on the desired thickness which, inturn, determines primarily the sensitivity of the polymer to adisturbance event. In general, the thicker the polymer the higher thethreshold necessary to trigger its performance. In FIG. 7, theperformance of a protection device according to one embodiment of theinvention is shown.

Next, at step 154, solvents are removed from the polymer and the firstelectrode is then attached to a second electrode, step 156. Preferably,adhesion is achieved without the use of a separate adhesion layer. Inone embodiment, this is accomplished using either a B or C stage epoxywhich is part of the solution forming the polymer. Use of such an epoxyallows adhesion to occur at partial cure in combination with heat andpressure which is applied, step 160, to cause the electrode layers to bebonded. Remaining solvents can be accomplished by raising thetemperature to approximately 120° Celsius which has been found toproduce a B stage polymer. Thereafter, the electrodes can be maintainedas is, step 162, or taken to final manufacturing, step 164, whichinvolves increasing temperatures, step 166, which are applied to thestructure and waiting for them to reach a final cure, step 168. At thispoint, the polymer is at C stage. For final manufacturing, an increasein temperature to approximately 180° Celsius has been found acceptablealthough this will vary with polymer.

Thus, the fact that a B or C stage epoxy (that is approximately 75%solvent and to which a number of fillers are added) is used provides adistinct manufacturing advantage in that low temperatures can be used toachieve good adhesion to the electrodes surrounding the polymer. Thisallows the cost effective manufacture of a laminated panel having alarge number of devices as demonstrated by the panel 100 of FIG. 3.

Referring to FIG. 4, process 150 continues at step 170 which involvesplacing a layer of resist on the laminated panel. Next, a photo imagecorresponding to the desired pattern is placed over the resist, step177, using well known PCB manufacturing techniques. Imaging can be doneto both sides of the panel simultaneously. This allows the imaging, step174, of a desired protection device pattern on the laminated panel formass production of large number of devices well suited to a large numberof applications. After imaging at step 174, the pattern is developed,step 176, and photo etched, step 178, using well known and costeffective PCB techniques.

It has been observed that after photo etching at step 178, the remainingresist can be left in tact, step 180, to serve as a protection layer orremoved, step 182, for further processing. For example, in certainapplications the photo resist can protect the electrode material duringplacement and mechanical attachment. An example of such an applicationwould include a multiple pin connector such as that shown in FIG. 6. Inother applications, the photo resist is removed for further processingof the devices which have been patterned to make the devices suitablefor use in the final application. An example here would include the useof protection devices on a printed circuit board where a solder coatingis applied to the electrodes to permit surface mounting of the devices.Alternatively, a conformal protective coating can be applied over eachdevice resulting in a standard manufacturing package. It should beunderstood that other standard manufacturing techniques may be employedto accommodate application of the protection devices.

In FIG. 6, a multi-pin connector 300 is shown receiving an array, suchas array 102, of protection devices according to the invention. Thearray 102 has been separated from a panel, such as panel 100, such thatmechanical attachment to the connector is facilitated. As shown, anarray consists of three layers 310, 312, 314 corresponding to the threelayers of a structure formed using the processes of the presentinvention. The first layer 310 provides the first electrode and, asshown, consists of 40 individually formed devices which accommodate pinsof the connector 300. It should be understood that many differentpatterns may be formed to suit other applications. Next, layer 312 isthe disturbance reacting substance, such as a polymer-based formulation,which is sandwiched between layer 310 and layer 314. Layer 314 providesthe attachment layer to the bottom of the connector 300 and provides asignal pathway to ground (via the ground pin not shown in FIG. 6) suchthat any one of the pins 316 can be protected during a disturbanceevent.

Pre-Etching of Pattern on Electrodes

As explained above and illustrated in the process figure diagrams, theuse of a electrode allows the use of standard PCB manufacturingtechniques. It is believed that an electrode-polymer-electrode layer canbe interspersed as a separate layer within a PCB or that such a three(3) layer structure, as described and illustrated herein, can belaminated on top of a PCB thereby providing total board and boardcomponent protection. This would be accomplished by burying of anelectrode-polymer-electrode layer within the PCB so that one electrodeis coupled to inputs of the PCB and the other electrode forms aconnection to ground (or a ground plane) of the PCB which is switchedupon the detection of a disturbance event. In practice,electrode-polymer-electrode layer could be implemented using standardmulti-layer PCB (layer in a board) layout techniques such as thru-holesand vias. This would also apply in flex circuit applications. If so, theelectrode surfaces would be pre-etched along desired signal routes andtraces in order according to the final board schematic and application.The first step would involve etching the electrode into whatever patternis desired. Depending on the application, whether it's a washer,connector, or standard surface mount profile component (0603, 0402,01206, or 0201 for example) both electrode layers would be etched. Sincea B stage epoxy can be used, attachment of the electrode surfaces toeach other can be readily accomplished with each pass of an electrodethrough a heat and pressure cycle.

Kapton Provides Improved Rigidity

It has been found that a thin layer of copper provides an excellentelectrode on which the polymer can be applied. According to anotherembodiment, the use of Kapton has been found to be advantageous becauseof the increased mechanical stiffness it provides. In some designs, thisresults in less overall capacitance since the plate to plate overlap canbe reduced due to the additional mechanical strength and rigidityprovided by the Kapton material. The reduced capacitance is desired inhigh frequency applications where added line capacitance can result inunwanted signal distortion. In addition, Kapton provides increasedstrength and rigidity to the three (3) layer structure further enhancinghandling during packaging and placement. Similar to the pre-etchingprocess described above, a sheet of electrode material (such as copper)having a pre-etched Kapton layer on one side can be used. The Kaptonlayer could be photo etched prior to lamination thereby providing thecorrect pattern for the particular application.

FIGS. 8 a and 8 b illustrate alternate embodiments of a protectiondevice using Kapton to increase rigidity. Specifically, the protectiondevice 200 of FIG. 8 a includes a full layer of Kapton 202 surrounding aburied first electrode 204 that sandwiches polymer-based formulation 206with second electrode 208. As before, a plated through-hole 210 providesthe pathway between first electrode 204 and second electrode 208 forsignal continuity when polymer-based formulation 206 achieves breakdownin response to a disturbance event. The physical dimensions of a devicehaving the characteristics of protection device 200 can vary but on 0603(6 mils×3 mils) has been constructed having a relatively low triggervoltage that causes breakdown.

FIG. 8 b illustrates a high voltage trigger of a protection device 230according to the invention.

Since Kapton is widely used as a patterned layer in many flexiblecircuit board designs, i.e. flex circuits, the use of an pre-etchedKapton layer 208 allows further simplification of the manufacturingprocess while providing device protection in a multitude of flex circuitapplications. The Kapton/electrode layer can be laminated to a secondelectrode layer 202 coated with a polymer 206 which is sandwiched inbetween thereby forming a Kapton/electrode-polymer-electrode structure.This eliminates the need for photo imaging with subsequent etching sincethe Kapton would already include the desired pattern. Moreover, Kaptonincreases the rigidity of the structure without the bulk and sizelimitations of a prior art substrate or reinforcement layer herebykeeping a relatively small profile for the entire device package. Inshort, until the present invention, no known way of providing total flexcircuit device ESD protection was available.

Essentials of a Polymer

The present invention also provides a device, in the form of a pressedor laminated structure that is able to react to a disturbance event,such as Electrostatic Discharge (ESD) or voltage surge, with measurednano-second response times thereby providing a discharge path to groundthat prevents damage to a protected component. It has been found that apolymer having application specific amounts of conductor dispersed withglass and Aluminum Oxide therein is capable of providing such afunction. It is believed that such functionality results directly from abreakdown in the resistive properties of the polymer which provides adischarge path through the conductive material in the event adisturbance event occurs. Thus, the polymer can switch from an open toshort circuit thereby discharging possible destructive signals away froma component to be protected. Compared with known prior art ESDprotection methods, the use of such a polymer is vastly superior inperformance and, using the manufacturing processes described above, canbe manufactured in quantity and at relatively low costs. Finally, it hasbeen verified that a protection component incorporating such a polymeris capable of withstanding multiple ESD events as well as with overvoltages greater than ESD and other disturbance events.

In general, formulating a polymer with these characteristics involvesconsideration of two primary aspects: viscosity and control offormulation properties.

Viscosity

The key variable is the use of a polymer having sufficient viscosity.Viscosity provides better dispersion and holds suspension. No precise orexact measure of viscosity can be specified although it can be comparedto a thick molasses or paste. A thickness has a direct impact on triggervoltage sensitivity, i.e. the voltage at breakdown of the insulatingproperties of the polymer is achieved and at which the polymer switchesfrom an open to a short, the thickness of the material is directlyrelated to performance. In general, the thicker the polymer, the greaterthe trigger voltage that must be applied in order to cause a breakdown.The addition of more conductor can be used to lower the breakdownvoltage of the material. This means that less tolerant devices wouldutilize a protection device with a thinner layer of polymer while moredurable devices can utilize a thicker layer. Ultimately, using theprocesses described above, the aim is to have a liquid that draws evenlywhen processed through a coating machine, on a screen printer orlaminator. A polymer according to the invention must possess thecharacteristic quality of being able to be spread out to achieve afairly uniform coat across the surface on which it is placed.

To better understand the formulating of a polymer with the desiredcriteria, reference is made to FIG. 5 which illustrates a formulationprocess, denoted generally as 250, for preparing such a polymer. Process250 involves the selection of a suitable polymeric solution, such as anepoxy, having a desired solvent level, step 252. For many applications,it has been found that an epoxy with an approximately 75% solvent levelis satisfactory but this is only an example and should not limit theinvention in any way. An example of such an Epoxy includes theScotch-Weld™ Epoxy Adhesive/Coating 2290 by 3M (Refer to Technical DataSheets dated June 2000 available from the 3M Company; 3M claimsScotch-Weld as its trademark) although it is believed that the processwill also work using a thermoset, thermoplastic, as well as otherpolymers such as polyethylenes, liquid crystal polymers, and acrylates.

Next, conductive materials are added to the epoxy, step 254, along withan antioxidant, step 256, an insulator, step 258, and the resultingsolution is mixed, step 260, until a desired viscosity level andrelative dispersion of the particles has been attained. It should beunderstood that variants in this process are contemplated including, forexample, the use of thin liquids, liquid and solid polymers.

In this way, the solution goes from an almost freely flowing liquidstate to a liquid having a very high viscosity. Again, no precisemeasure of viscosity nor mixing period can be specified, but the process250 can be applied to achieve a suitable polymer that is applicationspecific with subsequent verification of performance largely a matter oftrial and error. In practice, an automated commercial mixer can be usedto facilitate mixing of the solution to the desired viscosity.

In general, the conductor, antioxidant and insulator comprise very smallparticles that can be mixed to achieve a relatively uniform consistency.One known insulating material comprises antioxidants which add to theresistive properties of the polymer and helps separate the conductiveparticles from each other such that an open circuit is provided duringnormal operation. Therefore, a suitable formulation of a polymeraccording to one embodiment would consist of the following components byvol %:

-   -   67% epoxy    -   0.1% Aluminum    -   4.9% Glass Beads (Potter Industries)    -   28% Aluminum oxide

Since capacitance of the formulation is largely a byproduct of thefiller materials mixed in the polymer, variations in filler type, sizeand quantity have been observed to effect the capacitance of thepolymer. Therefore, depending on the restrictions which a particularapplication may have in terms of added capacitance, the filler type,size and quantity may be altered to guarantee a relatively uniform levelrange of capacitance values from one device to another within a panel.

Coating Methods

Coating of the polymer can be accomplished by either screen printing orby direct coating using a coating line. The major difference between thetwo processes lies in the way the polymer is dispensed unto theelectrode. With a screen printer, the polymer is dumped unto theelectrode surface and spread across the surface. Comparatively, on thecoating line, the material is extruded through a die head and theelectrode surface is passed about an area where the die head pumps thepolymer over the electrode resulting in an extremely uniform precisioncontrol of the coating process and the option to coat on a continuousbasis. Alternate coating line processes can also be used such as gravurerollers, for example.

Conductor Dispersion

It has been found that a variety of conductors can be mixed into thesolution including aluminum, aluminum oxide, and tungsten, a materialwith a very high melting point, as well as other conductive materials.Uniform dispersion of the conductor, however, should be attained whichis easy to achieve given the relatively low viscosity of epoxy solventsolution prior to mixing. The capability for mixing these materials hasbeen demonstrated using tungsten, aluminum, and silver coated glassbeads as conductive particles. Specifically, it has been observed thatthe use of aluminum oxide as a conductor drops the trigger voltage ofthe polymer. In essence, being able to use a variety of conductors, thedistance between the particles can be controlled and maintained veryclose, thereby defining a relationship between spacing of the particlesand trigger voltage.

The fact that a variety of conductors can be used provides flexibilityin design since different application may require different triggerlevels. Moreover, conductors do not have to be coated in order toinfluence their performance within the solution as the quantity ofconductor can be controlled and dispersed to effect performance.

Curing Epoxies

Curing

The transition period of an epoxy mixture from a liquid to a solid isgenerally labeled the cure time. It can be divided into threephases—open time or wet lay-up time (liquid state), initial cure (gelstate) and final cure (solid state). The speed of the reaction (and thelength of these phases and the total cure time) varies relative to theambient temperature.

Other Applications

It is anticipated that the methods of the present invention will haveapplication to the manufacture of other than protection devices. Forexample, the process may suggest ways of manufacturing widely usedpassive components such as resistors and capacitors, by changing thenature of the active fillers within the polymer formulation. Forresistors, the added filler material can be carbon-based while tantalummay be used for capacitors.

FIG. 7 is a graph illustrating the performance of a sample protectivedevice according to the invention. As above, the input voltage 300 goesfrom a nominal operating value to a spike 310 which mimics theoccurrence of a disturbance event. This could be replaced using a pulsegenerator having a 50 ohm transmission line output capable of generatingat least a 1500 V waveform (able to deliver a 30 amp square wave pulseto stimulate an 8000 V double exponential ESD pulse.) The device istriggered by the voltage spike 310 and, after breakdown, current throughthe device safely flows to ground as indicated by the fulling side ofthe spike waveform. Eventually, the output of the device clamps at point314 representing the clamping voltage of the protection device, a levelthat is presumably safe for the component being protected.

Use of Nanoparticles

It has been found that the use of nanometer sized aluminum particlesprovides some particular advantages in that no aluminum nor aluminumoxide is required to be added as a separate step. For example, suchnano-sized particles are available from TECHNANOGY and consist of 46.1nm sized aluminum particles (i.e. aluminum powder) with 63.7%nano-aluminum and the remainder consisting of aluminum oxide. Inaddition, it has been observed that for an 0603 device, the overalladded capacitance is decreased by almost half using such nano sizedparticles.

While the invention has been described with reference to illustrativeembodiments, this description is not intended to be construed in alimiting sense. Various modifications in combinations of theillustrative embodiments, as well as other embodiments of the invention,will be apparent to persons skilled in the art upon reference to thedescription. It is therefore intended that the appended claims encompassany such modifications or embodiments.

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 28. (canceled) 29.(canceled)
 30. (canceled)
 31. (canceled)
 32. (canceled)
 33. A device forprotecting an electronic component during the occurrence of adisturbance event comprising: first and second electrodes; and apolymer-based formulation interspersed between said first and secondelectrodes; wherein said polymer-based formulation is capable ofcreating a signal path from said first electrode to said secondelectrode in response to the occurrence of a disturbance event.
 34. Thedevice according to claim 33 wherein said first and second electrodescomprises layers made from a conductive material.
 35. The deviceaccording to claim 34 wherein said conductive material is chosen fromthe group consisting of: copper, beryllium copper, nickel, gold, orsilver.
 36. The device according to claim 34 wherein said form a panel.37. The device according to claim 36 wherein a pattern corresponding toa plurality of protection devices has been created on at least one ofsaid layers.
 38. The device according to claim 33 further comprising athrough-hole coupling said first electrode to said second electrode andproviding a signal path during a disturbance event.
 39. The deviceaccording to claim 33 further comprising a layer of Kapton coupled tosaid first electrode.
 40. The device according to claim 33 wherein saidpolymer-based formulation consists of a suitable polymer havingconductors, an antioxidant, and an insulator mixed therein.
 41. Thedevice according to claim 33 wherein said polymer-based formulationconsists of a suitable polymer having nano-sized aluminum particlesmixed therein.